Radiation measurement specialist Sun Nuclear (Melbourne, FL) showcased its recently released 3DVH dose verification and analysis system, designed for QA of intensity-modulated radiotherapy (IMRT) delivery.
The key feature of 3DVH is that it uses conventional QA data to predict the clinical impact upon the actual patient. It does this by importing measurements from Sun Nuclear's patient QA devices – including MapCHECK 1 and 2, ArcCHECK and EPIDose – and patient data received from the treatment planning system.
The patient data, which include plan, structure and dose information, are perturbed according to the errors measured in the QA analysis, using a patent pending algorithm called PDP (planned dose perturbation). According to Sun Nuclear's Will Nevins, perturbation offers an efficient and accurate alternative to performing a secondary dose calculation, which can itself introduce new errors.
The PDP algorithm reveals the impact of measured errors on patient dose and dose-volume histograms (DVHs). "Instead of the dose to a phantom, this shows the impact to the patient, it's a big step going from phantom to real patient geometry and it's very advantageous," said Nevins.
While conventional QA systems report an overall percentage pass rate, usually for dose-in-phantom, 3DVH displays and analyses dose-to-patient and DVHs for individual target structures and organs-at-risk. Viewing the dose to anatomical structures could prove invaluable, for example in situations where the overall pass rate is acceptable, but there's still underdosing of a target or over-irradiation of an organ-at-risk; or in cases where the conventional pass rate is low, but the impact on the patient dose/DVH is not detrimental.
"3DVH adds an additional dimension of QA that is more clinically relevant than traditional QA," Nevins told medicalphysicsweb.
Speed it up
IBA Dosimetry of Germany was highlighting the LDA-99SC – a linear diode array for use with its Blue Phantom2 3D water phantom. The device is said to considerably accelerate radiotherapy commissioning.
The linac commissioning process previously involved moving a point detector in 2 mm steps throughout the phantom volume. The LDA-99SC, on the other hand, with its array of 99 detectors, can measure a full 40 cm field profile in less than one second. According to IBA, the LDA-99SC also offers high data accuracy, due to high detector spacing resolution combined with an advanced multi-scanning routine that performs automatic shifts and measurements with an accuracy down to 0.5 mm.
"Linac QA is a time-consuming process for the medical physicist," explained Ralf Schira, IBA Dosimetry's vice-president of marketing. "Our customers have achieved up to three times faster commissioning, and this means a faster start to patient treatment."
Elsewhere, Modus Medical Devices (London, ON) was also focused squarely on speeding up the QA process. The Canadian manufacturer demonstrated its newly released Quasar eQA software, designed to simplify linac QA by using images from the electronic portal imaging device (EPID).
The software automates analysis and reporting for six important QA tests, most of which are recommended by the AAPM's TG 142 report. Images are checked remotely and the system reports pass or fail according to tolerances configured by the medical physicist. As well as linac testing, the system can also keep track of how the testing process is performed, and whether this changes over time.
"What we're trying to do is to implement automated image analysis and get rid of the film," said Modus' president John Miller. "Taking the film out and using EPID instead for linac QA saves a lot of time."